1. Field of the Invention
The present invention relates to a liquid-liquid extraction process, more particularly it relates to a provision of a novel process for extracting a metal ion M.sup.n.sup.+ from an aqueous dilute solution containing said metal ion(s) through a porous membrane impregnated with a chelating agent containing solution.
The present invention further relates to an apparatus used for the liquid-liquid extraction process.
2. Description of the Prior Art
The liquid-liquid extraction process which utilizes chemical equilibrium between a complexing reagent (e.g. liquid ion exchanger, chelating reagent, carboxilic acid compound, etc.) in an organic solvent immissible with water and a metal ion in an aqueous solution has been widely used in the field of analytical chemistry on a laboratory scale. This process has also been used in nuclear industry, and in extractive metallurgy in an industrial scale. In addition, the conventional liquid-liquid extraction process may be applicable to the treatment of waste water.
When the conventional solvent extraction process is carried out in an industrial scale, metal ions are firstly extracted from their aqueous solution by an extractor (e.g., mixersettler type extractor, continuous counter current column extractor), and the extracted metal ions are secondly stripped from the organic solvent layer into an aqueous phase. In such conventional processes, at least two steps and large scale equipment, e.g. towers, have necessarily been employed.
However, the conventional method is expected to be improved by bringing raw feed solution into contact with an absorption solution via a porous film impregnated with an organic complexing agent solution (i.e., liquid film) so that the two processes may be combined into one operation with a compact extractor-stripper equipment. Use of the liquid film will increase the efficiency of contact of a raw feed solution with an absorption solution by use of a bundle of tubes and baffles, no problem concerning separation of the solutions being involved. Such an improved process using a liquid film impregnated with an organic complex agent solution has not yet been found.